1. Field of the Invention
Embodiments of the present invention generally relate to an amorphous silicon (a-Si) seasoning process for silicon nitride film deposited on large-sized substrates in a batch process using a plasma enhanced chemical vapor deposition (PECVD) system.
2. Description of the Related Art
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition or CVD. Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired film.
An alternative method of depositing layers over a substrate includes plasma enhanced CVD (PECVD) techniques. Plasma enhanced CVD techniques promote excitation and/or dissociation of the reactant gases by the application of radio frequency (RF) energy to a reaction zone near the substrate surface, thereby creating a plasma. The high reactivity of the species in the plasma reduces the energy required for a chemical reaction to take place, and thus lowers the temperature required for such CVD processes as compared to conventional thermal CVD processes. The relatively low temperature of some PECVD processes helps semiconductor manufacturers lower the overall thermal budget in the fabrication of some integrated circuits.
One type of material that semiconductor manufacturers commonly deposit using PECVD techniques is silicon nitride. Silicon nitride films are used for a variety of different purposes in integrated circuits. For example, a silicon nitride film may be used as an insulating layer around transistor gates or a barrier layer between a premetal dielectric layer and the semiconductor substrate.
With the rapid growth in the large area panels, the ever-increasing substrate sizes create significant manufacturing challenges relative to reliable wafer-to-wafer repeatability and uniformity of deposited material layers. For example, in the conventional batch process for PECVD-deposited SiN films, differences in the rate of dissociation of precursor gases, fluctuations in the chamber pressure (which may occur when reactant species are introduced into the chamber), and/or increased chamber temperature may result in deposition rate variation and thus poor film thickness uniformity after the initial substrate is processed. As can be seen in FIG. 3, which illustrates a graph showing the film deposition rate (in Å/min) and film uniformity rate (in %) for a PECVD-deposited SiN film vary inconsistently as a function of the number of the substrates being processed. The thickness and the electrical properties of the film can vary across the diameter of each substrate and can also vary from substrate to substrate. It has been reported that this non-uniformity is even more severe for larger substrates of size measuring approximately about 3 meter by 3 meter in scale. Non-uniformity of the deposited layers limits yield and productivity of the deposition process, as well as overall performance of the integrated circuits.
While a frequent chamber cleaning (e.g., every 1-2 substrates) may be performed to stabilize the chamber conditions and thus improve the film thickness uniformity, the frequent chamber cleaning would reduce the overall throughput of the production line. Therefore, there is a need for depositing a silicon nitride material on large-sized substrates with better film uniformity and reliable repeatability while maintaining the substrate throughput.